The present invention relates to an electro-conductive resin composition, particularly to a resin composition used as a material for shielding electro-magnetic or electrostatic field or an antistatic or static dissipative material.
Hitherto, there have been used electro-conductive resins, in which one for shielding electro-magnetic or electrostatic field has a resistivity of about 10.sup.0 -10.sup.2 .OMEGA.-cm or less and the other for static dissipative materials has a resistivity of about 10.sup.4 -10.sup.11 .OMEGA.-cm. The electro-conductive composition material generally comprises a matrix resin blended with electro-conductive materials or fillers, which are mainly selected from the group comprising metal fibers such as stainless steel fibers, cooper fibers, aluminum fibers, brass fibers, nickel fibers and etc.. For instance, there is disclosed an electro-conductive resin containing metal fibers in U.S. Pat. No. 4,664,971.
On the other hand, the inventors has already proposed a new electro-conductive resin composition blended with zinc oxide whiskers in a tetrapod shape.
However, there are the following problems to be solved in the conventional resin composition blended with the metal fibers, such as stainless steel fibers.
Firstly, it is difficult to provide an article, if made of the above resin composition, with a stable electro-conductivity, because the metal fibers are hard to be uniformly dispersed in a resin matrix and thus to be fully distributed at a corner or narrow portion and also the mutual contact probability of the metal fibers comes to be small as the result of their orientation along the resin flow on molding.
Secondly, the electro-conductivity tends to be decreased owing to a cycle of cooling and heating, because the total number of mutual contact points is small and also there is a large volume difference between expanding and shrinking owing to the above cycle.
Thirdly, there are some problems of the article surface characteristics and coloring appearance.
On the other hand, when a resin composition comprises carbon fibers or powders, the color tone is limited to black and there are some problems from the view point of inflammability or burning resistance, as well as a problem of stable electro-conductivity.
Furthermore, there has been a high specific gravity and loading problem in an electro-conductive resin containing zinc oxide whiskers in a tetrapod shape.